Optically monitoring the microenvironment of a hydrophobic cargo in amphiphilic nanogels: influence of network composition on loading and release

Amphiphilic nanogels (ANGs) are promising carriers for hydrophobic cargos such as drugs, dyes, and catalysts. Loading content and release kinetics of these compounds are controlled by type and number of hydrophobic groups in the amphiphilic copolymer network. Thus, understanding the interactions between cargo and colloidal carrier is mandatory for a tailor-made and cargo-specific ANG design. To systematically explore the influence of the network composition on these interactions, we prepared a set of ANGs of different amphiphilicity and loaded these ANGs with varying concentrations of the solvatochromic dye Nile Red (NR). Here, NR acts as a hydrophobic model cargo to optically probe the polarity of its microenvironment. Analysis of the NR emission spectra as well as measurements of the fluorescence quantum yields and decay kinetics revealed a decrease in the polarity of the NR microenvironment with increasing hydrophobicity of the hydrophobic groups in the ANG network and dye-dye interactions at higher loading concentrations. At low NR concentrations, the hydrophobic cargo NR is encapsulated in the hydrophobic domains. Increasing NR concentrations resulted in probe molecules located in a more hydrophilic environment, i.e., at the nanodomain border, and favored dye-dye interactions and NR aggregation. These results correlate well with release experiments, indicating first NR release from more hydrophilic network locations. Overall, our findings demonstrate the importance to understand carrier-drug interactions for efficient loading and controlled release profiles in amphiphilic nanogels.

pH-responsive nanogels with enhanced antioxidant and antitumor activities on drug delivery and smart drug release

pH-responsive nanogels have played an increasingly momentous role in tumor treatment. The focus of this study is to design and develop pH-responsive benzimidazole-chitosan quaternary ammonium salt (BIMIXHAC) nanogels for the controlled release of doxorubicin hydrochloride (DOX) while enhancing its hydrophilicity. BIMIXHAC is crosslinked with carboxymethyl chitosan (CMC), hyaluronic acid sodium salt (HA), and sodium alginates (SA) using an ion crosslinking method. The chemical structure of chitosan derivatives was verified by 1H NMR and FT-IR techniques. Compared to hydroxypropyl trimethyl ammonium chloride chitosan (HACC)-based nanogels, BIMIXHAC-based nanogels exhibit better drug encapsulation efficiency and loading capacity (BIMIXHAC-D-HA 91.76 %, and 32.23 %), with pH-responsive release profiles and accelerated release in vitro. The series of nanogels formed by crosslinking with three different polyanionic crosslinkers have different particle size potentials and antioxidant properties. BIMIXHAC-HA, BIMIXHAC-SA and BIMIXHAC-CMC demonstrate favorable antioxidant capability. In addition, cytotoxicity tests showed that BIMIXHAC-based nanogels have high biocompatibility. BIMIXHAC-based nanogels exhibit preferable anticancer effects on MCF-7 and A549 cells. Furthermore, the BIMIXHAC-D-HA nanogel was 2.62 times less toxic than DOX to L929 cells. These results suggest that BIMIXHAC-based nanogels can serve as pH-responsive nanoplatforms for the delivery of anticancer drugs.

Rational Design and Development of Polymeric Nanogels as Protein Carriers

Proteins have gained significant attention as potential therapeutic agents owing to their high specificity and reduced toxicity. Nevertheless, their clinical utility is hindered by inherent challenges associated with stability during storage and after in vivo administration. To overcome these limitations, polymeric nanogels (NGs) have emerged as promising carriers. These colloidal systems are capable of efficient encapsulation and stabilization of protein cargoes while improving their bioavailability and targeted delivery. The design of such delivery systems requires a comprehensive understanding of how the synthesis and formulation processes affect the final performance of the protein. This review highlights critical aspects involved in the development of NGs for protein delivery, with specific emphasis on loading strategies and evaluation techniques. For example, factors influencing loading efficiency and release kinetics are discussed, along with strategies to optimize protein encapsulation through protein-carrier interactions to achieve the desired therapeutic outcomes. The discussion is based on recent literature examples and aims to provide valuable insights for researchers working toward the advancement of protein-based therapeutics.

Dual-reactive nanogels for orthogonal functionalization of hydrophilic shell and amphiphilic network

Amphiphilic nanogels (NGs) combine a soft, water-swollen hydrogel matrix with internal hydrophobic domains. While these domains can encapsulate hydrophobic cargoes, the amphiphilic particle surface can reduce colloidal stability and/or limit biological half-life. Therefore, a functional hydrophilic shell is needed to shield the amphiphilic network and tune interactions with biological systems. To adjust core and shell properties independently, we developed a synthetic strategy that uses preformed dual-reactive nanogels. In a first step, emulsion copolymerization of pentafluorophenyl methacrylate (PFPMA) and a reduction-cleavable crosslinker produced precursor particles for subsequent network modification. Orthogonal shell reactivity was installed by using an amphiphilic block copolymer (BCP) surfactant during this particle preparation step. Here, the hydrophilic block poly(polyethylene glycol methyl ether methacrylate) (PPEGMA) contains a reactive alkyne end group for successive functionalization. The hydrophobic block (P(PFPMA-co-MAPMA) contains random methacryl-amido propyl methacrylamide (MAPMA) units to covalently attach the surfactant to the growing PPFPMA network. In the second step, orthogonal modification of the core and shell was demonstrated. Network functionalization with combinations of hydrophilic (acidic, neutral, or basic) and hydrophobic (cholesterol) groups gave a library of pH- and redox-sensitive amphiphilic NGs. Stimuli-responsive properties were demonstrated by pH-dependent swelling and reduction-induced degradation via dynamic light scattering. Subsequently, copper-catalyzed azide-alkyne cycloaddition was used to attach azide-modified rhodamine as model compound to the shell (followed by UV-Vis). Overall, this strategy provides a versatile platform to develop multi-functional amphiphilic nanogels as carriers for hydrophobic cargoes.

Microgels and Nanogels for the Delivery of Poorly Water-Soluble Drugs

While microgels and nanogels are most commonly used for the delivery of hydrophilic therapeutics, the water-swollen structure, size, deformability, colloidal stability, functionality, and physicochemical tunability of microgels can also offer benefits for addressing many of the barriers of conventional vehicles for the delivery of hydrophobic therapeutics. In this review, we describe approaches for designing microgels with the potential to load and subsequently deliver hydrophobic drugs by creating compartmentalized microgels (e.g., core-shell structures), introducing hydrophobic domains in microgels, leveraging host-guest interactions, and/or applying "smart" environmentally responsive materials with switchable hydrophobicity. In particular, the challenge of promoting hydrophobic drug loading without compromising the inherent advantages of microgels as delivery vehicles and ensuring practically relevant release kinetics from such structures is highlighted, with an eye toward the practical translation of such vehicles to the clinic.

Influence of Nanogel Amphiphilicity on Dermal Delivery: Balancing Surface Hydrophobicity and Network Rigidity

Polymeric nanogels are promising nonirritating nanocarriers for topical delivery applications. However, conventional hydrophilic networks limit encapsulation of hydrophobic therapeutics and hinder tailored interactions with the amphiphilic skin barrier. To address these limitations, we present amphiphilic nanogels containing hydrophilic networks with hydrophobic domains. Two competing factors determine favorable nanogel-skin interactions and need to be balanced through network composition: suitable surface hydrophobicity and low network rigidity (through physical hydrophobic cross-links). To ensure comparability in such investigations, we prepared a library of nanogels with increasing hydrophobic cholesteryl amounts but similar colloidal features. By combining mechanical and surface hydrophobicity tests (atomic force microscopy (AFM)) with dermal delivery experiments on excised human skin, we can correlate an increased delivery efficacy of Nile red to the viable epidermis with a specific network composition, i.e., 20-30 mol % cholesterol. Thus, our nanogel library identifies a specific balance between surface amphiphilicity and network rigidity to guide developments of advanced dermal delivery vehicles.

In Vivo Biocompatible Self-Assembled Nanogel Based on Hyaluronic Acid for Aqueous Solubility and Stability Enhancement of Asiatic Acid

Asiatic acid (AA), a natural triterpene found in Centalla asiatica, possesses polypharmacological properties that can contribute to the treatment and prophylaxis of various diseases. However, its hydrophobic nature and rapid metabolic rate lead to poor bioavailability. The aim of this research was to develop a thermoresponsive nanogel from hyaluronic acid (HA) for solubility and stability enhancement of AA. Poly(N-isopropylacrylamide) (pNIPAM) was conjugated onto HA using a carbodiimide reaction followed by ¹H NMR characterization. pNIPAM-grafted HA (HA-pNIPAM) nanogels were prepared with three concentrations of polymer, 0.1, 0.15 and 0.25% w/v, in water by the sonication method. AA was loaded into the nanogel by the incubation method. Size, morphology, AA loading capacity and encapsulation efficiency (EE) were analyzed. In vitro cytocompatibility was evaluated in fibroblast L-929 cells using the PrestoBlue assay. Single-dose toxicity was studied using rats. HA-pNIPAM nanogels at a 4.88% grafting degree showed reversible thermo-responsive behavior. All nanogel formulations could significantly increase AA water solubility and the stability was higher in nanogels prepared with high polymer concentrations over 180 days. The cell culture study showed that 12.5 µM AA in nanogel formulations was considered non-toxic to the L-929 cells; however, a dose-dependent cytotoxic effect was observed at higher AA-loaded concentrations. In vivo study proved the non-toxic effect of AA loaded in HA-pNIPAM nanogels compared with the control. Taken together, HA-pNIPAM nanogel is a promising biocompatible delivery system both in vitro and in vivo for hydrophobic AA molecules.

Effect of TEOA on the Process of Photopolymerization at 532 nm and Properties of Nanogels

Nanogel is an important kind of biomaterials applied for wound dressings, drug delivery, medical diagnostics and biosensors. The properties of nanogels closely depend on the density of the crosslinking network. In this study, the role of triethanolamine (TEOA) in the effect on the crosslinking degree of nanogels based on poly(ethylene glycol) diacrylate (PEGDA) was investigated and illustrated. The effect of TEOA on the process of photopolymerization at 532 nm and properties of the nanogels was systematically investigated by using UV-vis spectroscopy, FT-IR spectroscopy, ¹ H NMR, DLS, SEM, AFM and DSC. In brief, the double bond conversion of photopolymerization and the crosslinking degree of nanogels can be effectively regulated by TEOA.

Sulfoxide-functionalized nanogels inspired by the skin penetration properties of DMSO

Among polymeric nanocarriers, nanogels are especially promising non-irritating delivery vehicles to increase dermal bioavailability of therapeutics. However, accurately tailoring defined interactions with the amphiphilic skin barrier is still challenging. To address this limited specificity, we herein present a new strategy to combine biocompatible nanogels with the outstanding skin interaction properties of sulfoxide moieties. These chemical motifs are known from dimethyl sulfoxide (DMSO), a potent chemical penetration enhancer, which can often cause undesired skin damage upon long-term usage. By covalently functionalizing the nanogels' polymer network with such methyl sulfoxide side groups, tailor-made dermal delivery vehicles are developed to circumvent the skin disrupting properties of the small molecules. Key to an effective nanogel-skin interaction is assumed to be the specific nanogel amphiphilicity. This is examined by comparing the delivery efficiency of sulfoxide-based nanogels (NG-SOMe) with their corresponding thioether (NG-SMe) and sulfone-functionalized (NG-SO2Me) analogues. We demonstrate that the amphiphilic sulfoxide-based NG-SOMe nanogels are superior in their interaction with the likewise amphipathic stratum corneum (SC) showing an increased topical delivery efficacy of Nile red (NR) to the viable epidermis (VE) of excised human skin. In addition, toxicological studies on keratinocytes and fibroblasts show good biocompatibility while no perturbation of the complex protein and lipid distribution is observed via stimulated Raman microscopy. Thus, our NG-SOMe nanogels show high potential to effectively emulate the skin penetration enhancing properties of DMSO without its negative side effects.

Enhancing the peroxidase-mimicking activity of hemin by covalent immobilization in polymer nanogels

A polymeric nanozyme that can closely mimic peroxidase is presented. The coordination between pendant hemins and primary amines together with the synergistic interactions between substrates and nanogels contribute to the enhanced catalytic activity.

Self-assembly of dual-responsive amphiphilic POEGMA-b-P4VP-b-POEGMA triblock copolymers: effect of temperature, pH, and complexation with Cu2+

Amphiphilic and dual-responsive triblock copolymer POEGMA-b-P4VP-b-POEGMA synthesized by RAFT self-assemble into spherical or interconnected micelles depending on the external stimulus and their complexation with Cu2+ results in responsive nanogels.

Amphiphilic Nanogels: Fuzzy Spheres with a Pseudo-Periodic Internal Structure

Amphiphilic polymer nanogels (NGs) are promising drug delivery vehicles that extend the application of conventional hydrophilic NGs to hydrophobic cargoes. By randomly introducing hydrophobic groups into a hydrophilic polymer network, loading and release profiles as well as surface characteristics of these colloids can be tuned. However, very little is known about the underlying internal structure of such complex colloidal architectures. Of special interest is the question how the amphiphilic network composition influences the internal morphology and the "fuzzy" surface structure. To shine light into the influence of varying network amphiphilicity on these structural features, we investigated a small library of water-swollen amphiphilic NGs using small-angle X-ray scattering (SAXS). It was found that overall hydrophilic NGs, consisting of pure poly(N-(2-hydroxypropyl)methacrylamide) (PHPMA), display a disordered internal structure as indicated by the absence of a SAXS peak. In contrast, a SAXS peak is present for amphiphilic NGs with various amounts of incorporated hydrophobic groups such as cholesteryl (CHOLA) or dodecyl (DODA). The internal composition of the NGs is considered structurally homologous to microgels. Application of the Teubner-Strey model reveals that hydrophilic PHPMA NGs have a disordered internal structure (positive amphiphilicity factor) while CHOLA and DODA samples have an ordered internal structure (negative amphiphilicity factor). From the SAXS data it can be derived that the internal structure of the amphiphilic NGs consists of regularly alternating hydrophilic and hydrophobic domains with repeat distances of 3.45-5.83 nm.

Production of lipophilic nanogels by spontaneous emulsification

Nanosized gel particles, so-called nanogels, have attracted substantial interest in different application fields, thanks to their controllable and three-dimensional physical structure, good mechanical properties and potential biocompatibility. Literature reports many technologies for their preparation and design, however a recurrent limitation remains in their broad size distributions as well as in the poor size control. Therefore, the monodisperse and size-controlled nanogels preparation by simple process -like emulsification- is a real challenge still in abeyance to date. In this study we propose an original low energy emulsification approach for the production of monodisperse nanogels, for which the size can be finely controlled in the range 30 to 200 nm. The principle lies in the fabrication of a direct nano-emulsion containing both oil (medium chain triglycerides) and a bi-functional acrylate monomer. The nanogels are thus formed in situ upon UV irradiation of the droplet suspension. Advantage of such modification of the oil nano-carriers are the potential modulation of the release of encapsulated drugs, as a function of the density and/or properties of the polymer chain network entrapped in the oil nano-droplets. This hypothesis was confirmed using a model of hydrophobic drug -ketoprofen- entrapped into the nanogels particles, along with the study of the release profile, carried out in function of the nature of the monomers, density of polymer chains, and different formulation parameters.

Pentafluorophenyl-based single-chain polymer nanoparticles as a versatile platform towards protein mimicry

Pentafluorophenyl-single chain polymer nanoparticles are readily conjugated with functional amines enabling facile SCNP modification, adjustment of physicochemical properties, and even protein mimicry.